The present invention is related to an improved system for managing air build-up in a transmission oil pump during shutdown of the vehicle.
The flow of transmission fluid through and around a torque converter and transmission is especially sensitive to fluid leaks due to aging of the bushing or other sealed areas. These leaks can eventually cause an interruption of smooth operation between the engine, the torque converter and the transmission.
These problems are often exacerbated during start-up of a vehicle. Ironically, the problems on start-up are often caused by the problems arising after shutdown of the vehicle. A torque converter is ideally fitted with a check valve to keep the torque converter full of fluid when the engine is shut down. However, because of leaks in the bushings or other scaling surfaces, a fluid path can be created to drain transmission fluid out of the converter and back into the transmission. The effect of such drain over time, when the transmission is shut off, is to make the transmission feel as though it is slipping during initial takeoff when the engine is restarted. This slipping can occur over a period of several seconds and is certainly a cause of consumer complaint.
In order to understand how this slow takeoff or slipping occurs because of transmission leaks, it is necessary to understand the relationship between the transmission pump and the torque converter vis-a-vis the fluid flow upon start-up in a transmission and a torque converter.
FIG. 1 illustrates start-up pressure to include the clutch pressure and the transmission pump pressure which, as illustrated, immediately or rather quickly ramps up to operating pressure. On the other hand, the torque converter input pressure increases more gradually than the pump pressure and the torque converter output pressure reaches its peak value on a slope similar to the torque converter input pressure.
All of these pressures, in an ideal situation are transmission fluid pressures. However, in the above discussed leakage problem where fluid drains out of the converter and into the transmission, the pressure illustrated by the torque converter output is partially an air pressure. Because this is air pressure, it can easily escape into or blow-by the face of the transmission pump. If the transmission pump were perfectly machined with the housing, the air would not be able to blow across the face of the pump. However, as a transmission pump and housing may be entirely adequate to prevent leakage of fluid, it can still allow the air to blow across the face of the pump. Having the air blow across the face of the pump has the effect of washing out fluid which is used to prime the pump on start-up. It also alters the path for the air discharge from the pressure side of the pump and becomes a source of air to feed the suction side of the pump. In effect, this buildup of air pressure at the ID (inside diameter) of the transmission pump causes the aforementioned slipping in the transmission upon initial takeoff for a number of seconds. In other words, the transmission pump should be primed with transmission fluid for an immediate xe2x80x9ctakeoff.xe2x80x9d However, because of the washing away of this fluid by the air pressure buildup which has leaked into the ID of the transmission pump, there is no effective noncompressible primer for the pump so that it delays pressure build up and causes the resultant slippage.
It is an object of the present invention to provide an arrangement to solve this slippage problem.
It is a particular feature of the present invention that the slippage of the transmission is prevented by a controlled release of air pressure built up at the ID of the transmission pump.
The objects of the present invention are accomplished by the use of a properly sized and positioned ball check air valve arrangement position between the ID of the transmission pump and the inside non-fluid containing areas of the transmission.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.